The addition of metal salts of .alpha.,.beta.-ethylenically unsaturated carboxylic acids to rubber compounds is known. U.S. Pat. No. 4,082,288, for instance, discloses a method for making molding compositions useful for manufacturing golf balls which includes the step of mixing a zinc oxide-methacrylic acid reaction product with a free-radical crosslinkable elastomer.
U.S. Pat. No. 4,191,671 is directed toward abrasion resistant rubber compositions having improved flexing fatigue resistance which are prepared by heating and curing a mixture comprising a diene elastomer, an unpolymerizable carboxylic acid or metal salt thereof, an .alpha.,.beta.-ethylenically unsaturated carboxylic acid, a divalent metal compound and an organic peroxide.
U.S. Pat. No. 4,501,866 provides a continuous polymerization process for preparing high cis-1,4 polybutadiene including the steps of continuously feeding 1,3-butadiene in a hydrocarbon solvent to a reaction with a preformed .pi. allyl catalyst formed by mixing a carboxylated metal oxy borate compound with nickel or cobalt, an organoaluminum compound, an alcohol, a small amount of 1,3-butadiene and a hydrocarbon solvent and, a cocatalyst comprising a boron trifluoride complex with an alcohol.
U.S. Pat. No. 4,529,770 provides vulcanizable rubber compositions comprising a rubbery polymer, from about 2.5 to 20 parts by weight of zinc dimethacrylate and about 30 to 70 parts by weight of a filler.
U.S. Pat. No. 4,720,526 is directed toward a method of preparing cured rubber compositions having improved modulus properties. The method includes the steps of adding a metal methacrylate and a peroxide curing agent to a rubbery polymer and then curing the mixture.
Finally, Japanese Patent No. 63-223048 is directed toward a process which involves mixing rubber, a metal oxide, hydroxide or carbonate, acrylic acid and a solvent for the rubber. In this manner a rubber crosslinking agent, e.g., zinc diacrylate, is formed that is free from dust. Improved physical properties are imparted to the rubber products.
Despite the widespread use of such metal salts in rubber polymer compounds the art has not provided a satisfactory method heretofore, for the uniform distribution of the metal salt throughout the polymer.